1. Field of the Invention
The invention relates to a transient voltage detection circuit and, more particularly, to a voltage detection circuit for system-level transient noise.
2. Description of the Prior Art
With the increasing operating speed and more integrated functions, electronic products are becoming more vulnerable to external noises like electromagnetic interference (EMI), system-leveled electrostatic discharge (ESD), electrical fast transient (EFT) events, etc. Those numerous noise signals may cause undershoot on power-supply or overshoot on ground-line voltages of a system, and even crash down the whole system. To meet the component-level ESD reliability, protection circuits like on-chip ESD protection circuits have been added to the I/O cells and power (VDD and VSS) cells of CMOS ICs. Moreover, in order to protect the system against system-leveled ESD events, additional discrete components like transient voltage suppressor (TVS) or varactor have been added to the system. If external noises cause voltage overshoot on the power supply, these additional discrete components can clamp down the overshooting voltage on the power supply line and hence protect the system against noises.
However, if the voltage undershoot is induced on the power-supply line, the system is easily hanged up by the noise due to unexpected voltage levels on nodes of internal circuits. The unexpected voltages on internal circuits can also induce mal-function of the system, which can be a serious safety issue especially when it is part of on-board systems of an automobile.
In practical applications, the ESD protection system can be implemented within electronic devices for protecting the electronic devices from being damaged by the unexpected ESD current. Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating an ESD protection system 1 in prior art. As shown in FIG. 1, the ESD protection system 1 includes ESD detection circuit 10, a transistor switch 12 and a system-restoring module 14. The ESD protection system 1 is coupled between a high voltage line Vdd and a low voltage line Vss, for protecting an internal working circuit 2.
Under normal operating condition, the high voltage line Vdd and the low voltage line Vss are utilized to provide a working voltage for driving the internal operating circuit 2, such that the internal working circuit 2 may fulfill its function successfully. In the meantime, the ESD system 1 is disabled.
When an abnormal signal (e.g. a strong transient voltage) occurs between the high voltage line Vdd and the low voltage line Vss because of the ESD phenomenon, the ESD detector 10 may detect the transient voltage and turn on the transistor switch 12. The transistor switch 12 is used for forming a discharging pattern between the high voltage line Vdd and the low voltage line Vss, for conducting the electrostatic discharge current Iesd. In practical applications, traditional ESD detection circuit 10 can be a transient voltage suppressor (TVS) diode or a varactor.
On the other hand, when the transient voltage is detected by the ESD detection circuit 10, the ESD detection circuit 10 may drive the system-restoring module 14, for rebooting or initial-restoring the internal working circuit through system-restoring module 14, so as to recover the internal working circuit 2.
Based on aforesaid examples, we may discover that the electronic system needs a stable and effective detection circuit, which must be able to detect and response to the system-leveled transient voltage (e.g. EMI, ESD and EFT) quickly, in order to trigger the electronic system to perform the following protective action. The invention discloses a transient voltage detection circuit, which can detect various types of system-leveled transient voltage, so as to solve aforesaid problems.